1. Field of the Invention
This invention relates to a fully encapsulated metal lead for multi-level interconnects for semiconductor applications and to the metal lead.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices, typical cross-sectional profiles of advanced multi-level metallization leads have been in the shape of an I-beam. In general, the lead is formed over an oxide layer and is connected to silicon or the like beneath the oxide layer through a via extending through the oxide layer which is filled with tungsten. This is accomplished by depositing a layer of titanium nitride into the via and over the oxide followed by a layer of chemically vapor deposited (CVD) tungsten (W) which fills the via and may extend over the titanium nitride. The tungsten is etched back in standard manner to leave tungsten only within the via as well as a layer of titanium nitride within the via and over the oxide. A layer of titanium nitride is then deposited, followed by a layer of aluminum alloy (about 0.5% copper (Cu) and then followed by a layer of titanium nitride. The upper layer of titanium nitride is then masked and an etchant is used to etch through the layers of titanium nitride, aluminum and the titanium nitride. Since the aluminum etches more rapidly than the titanium nitride, there is provided an I-shaped lead with exposed outer aluminum surfaces having an upper anti-reflective titanium nitride layer, etc., an intermediate aluminum alloy layer and a lower barrier metal layer of titanium nitride, titanium tungsten, etc.
A problem with leads having exposed surfaces is that of electromigration, though other properties of such leads can also be improved as will be discussed hereinbelow.